Debug.exe Writing to sectors

[Etienne Marais]

I have studied most of the commands and features available in debug.exe now, but I am curious to why and when one would like to make use of the w 'write' version where you can specify the start sector of the disk. Is this for very low level stuff only ?

[Kerr-Mudd, John]

On Wed, 4 Jan 2023 02:15:58 -0800 (PST)
Etienne Marais <etienne...@nospicedham.gmail.com> wrote:

> I have studied most of the commands and features available in debug.exe now, but I am curious to why and when one would like to make use of the w 'write' version where you can specify the start sector of the disk. Is this for very low level stuff only ?
>

Yes. I used to use it to edit floppy disk bootsectors. (we'd get some
boot sector viruses come in at times).



--
Bah, and indeed Humbug.

[Terje Mathisen]

I once fixed a laptop over a sat phone link to an oil engineer working
somewhere in a Middle East desert: The Master Boot Record (MBR) had been
scrambled by a bad software crash, but I was able to get him to boot up
with a Dos floppy, enter DEBUG and then enter commands to load & list
that MBR, figure out what was wrong (I was looking at a similar laptop
in Oslo) and tell him how to enter hex bytes, verify them and then write
them back to the hard disk.

His PC booted again on the first try. :-)

Terje

--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

[wolfgang kern]

On 04/01/2023 11:15, Etienne Marais wrote:
> I have studied most of the commands and features available in debug.exe now, but I am curious to why and when one would like to make use of the w 'write' version where you can specify the start sector of the disk. Is this for very low level stuff only ?

even cumbersome to enter everything in hexadecimal and in consecutive
order debug.com was absolute the best way to create my very own tools
and the core of my first OS (~1980)

Yes, it is really the lowest level possible for programming.
But it can also be a life saver for complete sector restore.
(you need to know and be aware of CHS and LBA formats)

I wrote my whole OS [KESYS] in hexadecimal and ASCII only.
But my own tool gave me much more comfort than DOS-debug:
* immediate disassemble for input verify
* allow full navigation within set limits (ie: go back up).
* can change between 16/32/64bit code interpreter anytime.
* toggle between ASCII/HEX input and dump view as well.
* RD/WR from/to any media, incl. partial sector writes.
* and a few more :)

unfortunately it became all history now (damned UEFI)
__
wolfgang

[Etienne Marais]

wow

I would feel proud as punch had I achieved that

[Etienne Marais]

Gonna Github it ?

[wolfgang kern]

On 05/01/2023 16:29, Etienne Marais wrote:
[...about my OS]

>> unfortunately it became all history now (damned UEFI)

> Gonna Github it ?

No, because of several things:
* it's a commercial product and still active >100 times
* it is written w/o any textual source code (hex only).
* it wont run on any newer PC (due UEFI) and also not on
many older stuff because it's made for specific hardware
where it was delivered on.
* I have only a handful copies on CD yet which I reserved
in case of required re-installation at clients side. And
my responsibility for maintenance times out end of 2025.

If I'm still alive I may share code snips and layout hints then.
__
wolfgang

[Etienne Marais]

Cool. Sounds like something for a very specific market if I may garner a guess. The switching between architecture looks very interesting, but I wonder how many people would make use of something like that in the 'real world'. Only reason I'm on x86 assembly is it satisfies my retro computing indulgence and desire to understand the evolution of architecture. I think I would enjoy such as tool but I doubt there are many people who would make good use of it (?)

[wolfgang kern]

I never offered my tools because they allowed everything w/o any
restriction and so could do a lot of damage if used by unaware.
And they are/were top hacker and best reverse engineering stuff :)

me too like to have historic PCs for playing my favorite old games.
but what's on the market is either badly damaged or heavy abused.

I searched w/o success for PC spare parts to revive any one of my
collection from the past. Nothing older than 3 years is available.
__
wolfgang

[Terje Mathisen]

I was just immensely relieved that I didn't have to try again, from
scratch. Afair I did get him to save that scrambled MBR sector to the
floppy, before starting to modify it, but it fortunately worked on the
first attempt.

[Robert Riebisch]

wolfgang kern wrote:

> I searched w/o success for PC spare parts to revive any one of my
> collection from the past. Nothing older than 3 years is available.

Are you really sure?
Where do you live?
What parts are looking for?

--
Robert Riebisch

[wolfgang kern]

Yes I'm pretty sure. Only second hand stuff w/o warranty are offered.
Vienna/Austria.
MSI Main-boards which can boot my KESYS (nonEFI, nonGPT) and accept
winXP+win7 ie: MSI 990FXA GD80 + CPU + DRAM. And a few older as well.

I need to purchase from nearby suppliers for warranty reasons,
all I ever bought from far distance was either wrong or damaged.
(I bought a "brand new" CPU from EBAY Germany recently: defective).

And because I could be sued if I repair client machines with unreliable
parts I closed the KESYS project and only maintain what's sold til end.
__
wolfgang